Form, fill and seal (FFS) packaging technology is widely used to package a broad variety of products including disposable medical devices, food stuffs and similar products. In one type of FFS packaging, materials corresponding to a lidstock for packages and a bottom or forming web are supplied in rolls. The forming web material is indexed from the roll into a heating zone where it is heated to forming temperatures. The heated forming web material is then either immediately formed or indexed into a forming station area where multiple box or cup shaped compartments are formed from the forming web using any one of a number of thermoforming techniques including drape forming, matched mold forming, vacuum forming or pressure bubble-plug assist vacuum forming. Other thermoforming methods are also known.
After forming, the bottom web is typically chilled or cooled and the product to be packaged is inserted into the individual formed compartments. The lidstock material is then applied to the forming web, sealing the compartments. The lidstock material may be sealed to the upper perimeter of the individual compartments using an adhesive and/or by heat sealing. The thus formed serially connected packages are cut from the web and trimmed to the desired final shape. Secondary functions that are selectively integrated into the process include printing or decorating either before or after forming, embossing, notching, slotting, punching, labeling, counting and stacking.
FFS packaging technology is especially adaptable to packaging environmentally sensitive products such as disposable medical devices and certain types of food stuffs. In connection with packaging such materials, it is important that when the package is opened by peeling the lidstock from the forming web portion of the package, the integrity of the seal can be determined by visual inspection, confirming package sterility. Thus it is desirable that the portion of the lidstock seal area that is adhered to the forming web create a visible "frost" on the forming web when the package is opened by peeling the lidstock from the forming web. Preferably, the package is opened by applying a moderate constant force to peel the lidstock from the forming web without delamination, stringing or forming "angel hair" in the seal area in order to prevent contamination of the product and facilitate easy access inspection of the seal.
The ability to peel the lidstock film from the substrate bottom web through the application of a uniform relatively low peel force may be desirable in the case of individual or multiple serially connected packages. Preferably, the force required to separate the lidstock film from the substrate bottom web is in the range of about 0.25 to about 1.25 lbs./inch when tested in the manner hereinafter set forth. If excessive or non-uniform force is required to peel the film from the substrate, it is exceedingly difficult to open the individual packages and extract the packaged items in a controlled fashion either mechanically or manually.
A transparent lidstock or forming web is desired for some applications to allow visual inspection of the packaged product. Additionally, the lidstock preferably has sufficiently low adhesive properties to prevent the packaged articles from adhering to the film when the film is peeled from the substrate forming web.
In the case of certain products, it is also desirable to provide a lidstock with "pop through" properties. Thus, a product may be extracted from the package by flexing the package to punch the product through the lidstock material. Materials that exhibit high elongation properties typically do not allow the product to punch through. Rather such materials elongate and drape around the product when the package is flexed.
The pop through feature may be desirable in the case of relatively rigid products that must be packaged in a manner that facilitates rapid extraction of the product from the package as in the case of disposable medical devices. Preferably, such lidstock films evidence pop through properties such that elongation to puncture is less than about 1.5 inches when tested in the manner hereinafter described.
Some products also require sterilization. In recent years there has been a trend away from conventional sterilization techniques such as autoclaving or ethylene oxide treatment for sterilizing disposable equipment for hospital and medical use such as tubes, syringes, pipettes, vials and the like. Rather, sterilization with ionizing radiation such as electron beam or gamma radiation has evolved as a preferred method of sterilizing many types of disposable equipment for hospital and medical use. Ionizing radiation, however, can profoundly alter the molecular structure and macroscopic properties of polymeric materials such as polypropylene, polyethylene and propylene-ethylene copolymers. Exposure to ionizing radiation typically results in loss of physical properties, brittleness and discoloration. Consequently, materials used to package products that are subsequently sterilized with ionizing radiation, should be resistant to radiation induced.
Thus, there exists a need for films useable as lidstocks and forming webs in form, fill and seal applications to produce packages that may be opened with the application of moderate force to peel the lidstock from the forming web. Additionally, the physical properties of the lidstock film should be such that a rigid product can be punched through the film without excessive elongation of the film.
There also exists a need for a lid stock film that provides a frosty or visually traceable indicator of seal integrity when a package is opened by peeling the lidstock away from the forming web. In conjunction with the lidstock, there exists a need for a forming web heat sealable to the lidstock to provide a product package with desirable properties, such as resistance to radiation induced loss of physical properties, brittleness and discoloration.